Ah, the mod was me. First of all, thank you for coming here and posting such a calm and constructive question. And I'm sorry, I certainly didn't intend to discourage you from participating! However, I am afraid that yes, deleting was indeed the right course of action. I know this can be confusing to new users (I remember how confusing I found it at first), but these sites don't work in the same way as traditional online forums. We don't do discussion and everything posted as an "Answer" needs to be a direct, preferably complete, answer to the question asked in the "Question".
In this case, the person who posted the question (the "OP", original poster) who is also new and so didn't know the rules, posted a second question as an answer to their original post. This is really something we want to avoid. The whole point of the Stack Exchange (SE) system is to have direct Questions and Answers. No discussions, no "noise", each post is a single question with one or more answers.
So yes, we really don't want people to be answering questions that were posted as answers and deleting is the standard course of action in such cases because we want to keep the site streamlined and to the point. As you spend more time on the various SE sites, and I hope you will despite the unpleasant first experience, you will see there is a general policy of aggressive deletion. Anything that isn't on topic or isn't directly answering the question asked will indeed be deleted.
You can think of these sites as having one main objective: to build a collection of useful Q&As that can then be used by others as a reference. So we want everything to be nice and clean and to the point so that if someone comes to a question two years down the line, they will just find a clear question and a clear answer and don't need to wade through several pages of discussion to find the one nugget of information they need as is often the case in traditional forums.
I completely understand how this can be surprising to new users, but this kind of strictness is a very important part of what makes these sites and this model work for us. Your answer was actually really good, it was just not an Answer to the Question of that page.